The present invention relates generally to a device for compensating a tensile yarn force sensor and, more particularly, to such a device having a measuring member by means of which the tensile force of a traveling yarn is detected at a work station of a multi-station textile machine in the course of being wound on a cheese, and wherein during the detection process the traveling yarn is arranged in a measuring position such that its exerts a measurable pressure on the measuring member.
When producing a cheese, for example on an automatic open-end spinning/winding machine, the yarn feed device thereof is usually set to provide a uniform yarn feed. Therefore the cheese could theoretically run at a constant circumferential speed. In actuality, however, fluctuations of the yarn tension occur. These fluctuations result, for example, from the oblique placement of the yarn in the course of the cross winding of the yarn, from piecing processes, and from restarting processes following a yarn break. Possible effects of a malfunction can be compensated by controlling the drive mechanism of the cheese as a function of the yarn tension.
Thus, the yarn tension is of great importance for the quality of the cheese. The winding tension is often regulated by adjusting the number of revolutions of the cheese in the winding device as a function of the yarn feed speed determined by a yarn feed device. If it is intended in this manner to assure the adherence to the winding tension by the use of mathematical functions, it is necessary to take yarn-specific factors into account, such as material, yarn number, yarn twist or yarn tension, which can have a strong effect on the result. In cases in which the tension is only empirically determined, the result is not always sufficiently accurate. In contrast thereto, exact measurement results without a loss in time are available when the yarn tension is detected by means of a tensile force sensor.
Tensile yarn force sensors have been known for a long time in connection with textile machines and are used, besides the measuring of the yarn tension, also to detect yarn breaks, or directly for controlling the tensile yarn force by means of a yarn tensioner. Such tensile yarn force sensors are known, for example, from German Patent Publications DE 41 29 803 A1 or DE 195 44 202 A1. German Patent Publication DE 195 44 202 A1 shows a winding station of an automatic winding device with a tensile yarn force regulating device, by means of which the yarn tension can be regulated to a desired value. A comb tensioner performs the function of a yarn tensioner and the function of a tensile yarn force sensor. German Patent Publication DE 41 29 803 A1 describes a tensile yarn force sensor for a textile machine which is suitable for measuring the tensile yarn force of rapidly moving yarn, and by means of which high-frequency tensile yarn force fluctuations can also be detected.
In order to prevent a loss of the quality of the cheese, it is necessary to assure the adherence to the respectively required winding tension. To this end the precise functioning of the tensile yarn force sensor and a dependable measurement result must be assured. One of the prerequisites for receiving a dependable measurement result is the elimination of external influences on the measuring system. External influences, for example thermal changes, lead to errors in the measuring signal. Compensating devices and compensation methods, which assure the stability of the measurement results over several hours, can only be found in expensive laboratory measuring systems. No use is made of such compensating devices in connection with mass-produced machines, in particular at the work stations of a multi-station textile machine, for economical reasons because of the high cost of such compensating devices. However, the external influences can be eliminated in a less elaborate manner by a zero compensation.
In case of a yarn break or a cop change in a winding machine, the measuring member of the tensile force sensor is not acted upon by any force. Therefore this phase is suitable for performing a zero compensation. If a zero compensation is performed after every yarn break or cop change, it is possible to expect at most approximately ten minutes until the next zero compensation, even at long cop running times. This is sufficient for many designs of tensile force sensors and leads to usable results.
Considerably longer running times without a yarn break or a feed cop or finished bobbin change occur in connection with automatic spinning/winding devices of the type for producing cheeses or in the course of yarn withdrawal from a cheese in a winding machine. As a result, the phases during which no force is exerted on the measuring member of the tensile force sensor are more infrequent, and therefore considerably longer intervals occur between successive zero compensation operations. This leads to an impairment of the dependability of the results in the course of determining the tensile yarn force, and can result in an undesired lack of quality of the cheese.
OBJECT AND SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a device for compensating a tensile yarn force sensor which will reduce or prevent the above disadvantages and will improve the dependability of the results of the determination of the tensile yarn force. This object is attained by means of a device wherein a zero compensation can be automatically initiated at preselectable times by means of a control device which, at the selected times, actuates an intentional cutting of the traveling yarn and actuates the performance of a zero compensation at the respective measuring member which has thereby been relieved of any yarn tension input. Thus, performance of a zero compensation is no longer tied to an interruption of the yarn travel by a bobbin or cop change, a yarn break or by a cleaning cut triggered because of a lack of quality. The intervals between successive zero compensations can be limited to a value which reduces external influences to a minimum or even totally compensates these influences. It is possible in this manner to prevent an impairment of the dependability of the results in the course of determining the tensile yarn force, or the dependability of the results can be improved.
A yarn cleaner, which is already present at the work station in conventional machines, is preferably controlled by the control device to execute the periodic cleaning cuts for actuating a subsequent zero compensation upon each such yarn cut. Advantageously, therefore, the present invention uses available existing components.
The unavoidable interruptions caused by bobbin and cop changes, yarn breaks or cleaning cuts triggered because of a lack of quality, can be used for additional zero compensations. Thus, the control device of the present invention preferably does not trigger the performance of a zero compensation at regular intervals, but rather only after a preselectable period of time elapses since the termination of the last zero compensation. Following an unplanned zero compensation, the next preplanned zero compensation can, for example, be advantageously delayed until a later time without having to accept disadvantages in connection with the dependability of measuring. This aids the achievement of the highest possible productivity.
As will thus be understood, the device of the present invention makes it possible to prevent the impairment of the dependability of the measured result of a tensile yarn force sensor in various textile yarn handling operations, e.g., in the course of drawing off yarn from a cheese of a winding machine, or in connection with automatic spinning/winding devices, which produce cheeses.
Further details, features and advantages of the present invention will be described and understood from the disclosure of an exemplary embodiment of the invention set forth below with reference to the accompanying drawing.